CODEWITHSUNDEEP
javaandroidmultithreadinguser-interface
Tech Nerd
Tech Nerd

Reputation: 832

Update the UI outside the main thread

I am totaly new to android and just want to know if it is any working and possible way to update the UI outside the main thread. Just from my code I have listed below I know that from this code; It is not possible at all. But, the thing is I just want to update the UI using another thread. Please help me thanks in advance!

 package com.example.app;

 import java.util.Random;
  import android.os.Bundle;
  import android.app.Activity;
  import android.view.Menu;
 import android.view.View;
  import android.widget.Button;
 import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends Activity {
private Button b;
public ImageView I1;
 public ImageView I2;
 public ImageView I3;
public ImageView I4;
public TextView T;
public TextView s;
@Override

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

 I1=new ImageView(this);
 I1=(ImageView) findViewById(R.id.imag1);
 I1.setVisibility(View.INVISIBLE);

 I2=new ImageView(this);
 I2=(ImageView) findViewById(R.id.imag2);
 I2.setVisibility(View.INVISIBLE);

 I3=new ImageView(this);
 I3=(ImageView) findViewById(R.id.imag3);
 I3.setVisibility(View.INVISIBLE);

 I4=new ImageView(this);
 I4=(ImageView) findViewById(R.id.imag4);
 I4.setVisibility(View.INVISIBLE);

 T=(TextView)findViewById(R.id.time);
 s=(TextView)findViewById(R.id.score);

Thread t=new Thread(new MyThread());
t.start();
  }

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

private class MyThread implements Runnable{
Random randomGenerator = new Random();
int n;
public void run(){

    while(true){
        n=randomGenerator.nextInt(8);

        if(n==1){
            I1.setVisibility(View.VISIBLE);

        }
        if(n==2){
            I2.setVisibility(View.VISIBLE);
        }

        if(n==3){
            I3.setVisibility(View.VISIBLE);
        }

        if(n==4){
            I4.setVisibility(View.VISIBLE);
        }
        try {
            Thread.currentThread().sleep(500);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
             e.getStackTrace();
        }
    }

   }




   }
   }

Upvotes: 0

Views: 9665

Answers (5)

Bijay
Bijay

Reputation: 11

A worker thread never can update main thread because only main thread can render the UI elements (TextView, EditText etc.) and if we try to update for sure we are going to an exception.

myAcitity.runOnUiThread(new Runnable() {
    public void run() {
        //here you can update your UI elements because this code is going to executed by main thread
    }
});

Otherwise you can use post method of View class

myView.post(new Runnable() {
        public void run() {
            //here you can update your UI elements because this code is going to executed by main thread
        }
    });

Upvotes: 1

mikeswright49
mikeswright49

Reputation: 3416

Use activity.runOnUiThread 

Acivity.runOnUiThread(new Runnable() {
    public void run() {
        //something here
    }
});

Upvotes: 3

Michal Dobrodenka
Michal Dobrodenka

Reputation: 1144

Only main thread can update UI. If your thread want to update UI, use activity.runOnUiThread()

However your action is just queued to run in UI thread(if you are running it not from UI thread), which mean it can update UI a little bit later.

http://developer.android.com/reference/android/app/Activity.html#runOnUiThread(java.lang.Runnable)

Upvotes: 0

Rodion Altshuler
Rodion Altshuler

Reputation: 1783

You can't update UI directly from non-UI thread, but You could communicate with UI thread using Handler object or AsyncTask object. The most convinient way to use AsyncTask:

  1. .doInBackground() method of AsyncTask runs in non-ui thread
  2. .onProgressUpdate() runs in UI thread so could change views
  3. You could use publishProgress() method inside doInBackground() to pass data to .onProgressUpdate.

Sorry if some mistakes in method names. Read http://developer.android.com/guide/components/processes-and-threads.html for details.

Upvotes: 3

Blackbelt
Blackbelt

Reputation: 157487

you have to use an Handler instance and use the post method do add a Runnable inside the queue of the UI Thread. If you are inside an Activity you can use runOnUiThread that is a "shortcut" to do the same thing

Upvotes: 0

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